Direct injection (DI) engines may produce more soot than port fuel injected engines in part due to diffuse flame propagation. As a consequence of diffuse flame propagation, fuel may not adequately mix with air prior to combustion, resulting in pockets of rich combustion that generate soot. Further, DI engines may be susceptible to generating soot during high load and/or high speed conditions when there is a lack of sufficient air and fuel mixing.
The inventors herein have recognized various issues in applying particulate filters to DI, spark-ignition engines. For example, it can be difficult to maintain accurate emission control during particulate filter regeneration in a DI, spark-ignition engine.
Thus, methods and systems for controlling operation of exhaust of an engine including a particulate filter are described herein. One exemplary method includes generating a vacuum during engine operation and storing the generated vacuum. Ambient air can be drawn through the particulate filter via the vacuum during and/or after engine shutdown to at least partially regenerate the particulate filter.
By performing the regeneration during and/or after engine shutdown, the particulate filter can be regenerated by an increased flow of oxygen to the particulate filter while avoiding potential increased emissions from a three-way catalyst in an exhaust tailpipe.
In one example, the vacuum may draw fresh air in a reverse direction through the filter. By controlling the system to draw fresh air into the particulate filter in a direction that is the reverse of a direction of exhaust flow during engine combustion, improved removal of soot may be achieved.
Yet another potential advantage of regenerating the filter during and/or after engine shutdown using stored vacuum is that a regeneration reaction can be delayed or advanced to a time when particulate filter conditions are appropriate for carrying out the regeneration reaction. For example, the stored vacuum may be stored until the particulate filter temperature becomes hot enough to carry out the regeneration reaction due to natural temperature increases that can occur after an engine shutdown. Further still, particulate filter regeneration may be selectively carried out under particular engine shutdown conditions (e.g., shutdowns in which filter regeneration is already commenced during engine running conditions, or shutdowns in which filter temperature is high enough), and not during others.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.